DN Ice Boat #2: Strange behaviour in the fir sides....

First I’ll update you as to the the wood I used. I talked to my friend and he reminded me what we made it with. The sides and bulkheads are fir, with marine ply to skin them. And the plank (which I don’t have a picture of yet) is laminated with Ash/Cherry/Ash. It’s got some nice shape to it, I’ll post a pic of it soon.

Anyways, I’m looking for some advice here:

The first picture is the ‘left hand’ side of the crack or whatever it is. It’s not as bad, but the right hand side of this same anomaly is the next pictures. This is one of the fir sides. I’m not sure how to deal with this. It doesn’t really like to push in with hand strength on the right side. I wonder if there is sawdust jammed in there. If I Was going to paint this, I’d chip the piece out and fill it with epoxy, but I’d like to keep a nice wood finish. The only possible solution I can think of is to put in some sort of a decorative inlay – and match it on both sides. I don’t even know what happened. It’s been sitting up in the rafters of shed for months waiting for more time. I wonder if it came because of the stress on the fir from being curved?